1. Field of the Invention
The present invention relates to a liquid discharge head, a manufacturing method thereof, and a microelectromechanical device.
2. Related Background Art
In a conventional liquid discharge head as an example of a microelectromechanical device for use in an ink-jet printer or the like, liquid is discharged from a discharge port by pressure generated by means of heating and thus bubbling the liquid in a liquid flow path. In order to heat the liquid, a heater for discharge is disposed on an element substrate. Driving voltage is supplied to the heater for discharge through wirings on the element substrate.
Recently, with regard to such a liquid discharge head, a structure has been proposed where, for the purpose of introducing most of the bubble to the side of the discharge port to improve the discharge efficiency, a cantilever-like movable member with one end thereof being supported is disposed in the liquid flow path. One end of the movable member is fixedly supported on the element substrate while the other end extends into the liquid flow path. In this way, the movable member is structured so as to be held at a certain distance over the element substrate and so as to be movable in the liquid flow path by the pressure generated by bubbling or the like.
Japanese Patent Application Laid-Open No. 10-76659 discloses, among liquid discharge heads having the above-mentioned movable member in the liquid flow path, one where the movable member is provided with a heater for discharge.
However, as shown in FIG. 14, in the heater for discharge disclosed in Japanese Patent Application Laid-Open No. 10-76659, electrothermal converting member electrodes 1204 and 1205 are formed so as to be folded back along the surface of the movable member. When the electrothermal converting members are laid out in this way, the position of the heater 1206 for discharge is unsymmetrical in the width direction of the movable member, which results in the tendency for the movable member to be distorted in bubbling, and thus, there are some cases where the durability of the movable member is not necessarily satisfactory. In addition, since the width of the electrodes is not sufficient, the structure is not suitable for passing heavy current therethrough.
Accordingly, an object of the present invention is to provide a liquid discharge head and a microelectromechanical device with satisfactory durability and reliability where a movable member in a liquid flow path comprises a heater for discharge.
According to an aspect of the present invention, there is provided a liquid discharge head comprising a substrate, a ceiling plate bonded to the substrate, a liquid flow path formed between the substrate and the ceiling plate, and a cantilever-like movable member having a fixed end fixed to the substrate and a free end extending into the liquid flow path, wherein the movable member is formed of a lower protective layer, a heat generating resistive layer, a lower electrode layer, an insulating layer, an upper electrode layer, and an upper protective layer stacked from the side of the substrate in the mentioned order, and wherein application of a voltage to a heat generating portion of the heat generating resistive layer causes bubbling of a liquid in the liquid flow path between the movable member an d the substrate to discharge the liquid.
According to another aspect of the present invention, there is provided a method of manufacturing a liquid discharge head which comprises a substrate, a ceiling plate bonded to the substrate, a liquid flow path formed between the substrate and the ceiling plate, and a cantilever-like movable member having a fixed end fixed to the substrate and a free end extending into the liquid flow path, the method comprising the steps of:
providing a space forming member on a substrate;
forming a movable member of a lower protective layer, a heat generating resistive layer, a lower electrode layer, an insulating layer, an upper electrode layer, and an upper protective layer stacked from the side of the substrate in the mentioned order; and
removing the space forming member to shape the movable member in the form of a cantilever.
According to still another aspect of the present invention, there is provided a microelectromechanical device comprising a cantilever-like movable member having a fixed end fixed to a substrate and a free end extending into a liquid flow path, wherein the movable member is formed of a lower protective layer, a heat generating resistive layer, a lower electrode layer, an insulating layer, an upper electrode layer, and an upper protective layer stacked from the side of the substrate in the mentioned order, and wherein application of a voltage to a heat generating portion of the heat generating resistive layer causes heating of a liquid in the liquid flow path.
It is to be noted that the upper electrode layer and the lower electrode layer are preferably formed of a high-melting metal.
The insulating layer is preferably made of SiN.
The heat generating resistive layer is preferably electrically connected to the electrode layers upstream and downstream with respect to the direction of discharge of the heat generating portion.
The upper electrode layer and the lower electrode layer are preferably formed so as to range from the front surface side to the rear surface side of the movable member.
Further, separately from the heat generating portion, the liquid flow path may further comprise therein a heater for adjustment provided correspondingly to the heater for discharge and a driver for the heater for adjustment for driving the heater for adjustment.
A voltage applied to the heater for adjustment may be lower than that applied to the heat generating portion.
The ceiling plate may be provided with a voltage converter to ensure that a voltage applied to the heater for adjustment is lower than a voltage applied to the heater for discharge.
A voltage applied to the heater for adjustment may be made lower than a voltage applied to the heater for discharge by connecting the heater for adjustment to a power source different from a power source connected to the heater for discharge.
A power source connected to the heater for adjustment may be common to a power source for a logic circuit.
The heater for adjustment may be provided on the downstream side with respect to the direction of discharge of the heater for discharge.
The heater for adjustment may be provided on the upstream side with respect to the direction of discharge of the heater for discharge.
A plurality of heaters for adjustment may be provided and they may be provided on the upstream side and the downstream side, respectively, with respect to the direction of discharge of the heater for discharge.
The area of the heater for adjustment is preferably smaller than that of the heater for discharge.
The area of the driver for the heater for adjustment is preferably smaller than that of the driver for the heater for discharge.
The signal generating portion of the driver for the heater for discharge may be the signal generating portion of the driver for the heater for adjustment.
The ceiling plate may further comprise a sensor for sensing the state in the liquid flow path corresponding to the heater for adjustment.
It is to be noted that the terms xe2x80x9cupstreamxe2x80x9d and xe2x80x9cdownstreamxe2x80x9d as used herein shall refer to the direction of the liquid flow from the supply source of the liquid through a bubble generating region (or the movable member) to the discharge port, or refer to the direction with regard to the structure related to the liquid flow.